Orthogonal Frequency Division Multiple Access (OFDMA)/Single Carrier-Frequency Division Multiple Access (SC-FDMA) systems are prevalent today. Typically, in an OFDMA system, the signals of several different users (i.e., entities that wish to communicate over the communication system) will each be assigned one or more unique subcarriers. Each subcarrier is generated and transmitted in a manner that allows all of the subcarriers to be transmitted concurrently without interfering with one another. Therefore, independent information streams can be modulated onto each subcarrier whereby each such subcarrier can carry independent information from a transmitter to one or more receivers.
Conventional OFDMA/SC-FDMA systems use a rectangular pulse shape, i.e., sinc in frequency, which has high side lobes. As a result, there are stringent synchronization requirements to maintain orthogonality. Timing advance signaling is required for synchronous multiple access, causing overhead. This overhead increases with the number of transmitters, which is a consideration in applications such as machine-type communication where a plurality of machines communicate with a base station. Moreover, OFDMA/SC-FDMA is highly sensitive to carrier frequency offset (CFO) mismatch between different electronic devices.
One way to avoid the aforementioned issues is to use Orthogonal Frequency Division Multiplexing/Offset Quadrature Amplitude Modulation (OFDM/OQAM), which has become popular in the wireless community recently. However, using OFDM/OQAM has issues such as peak to average power ratio (PAPR), Multiple-Input Multiple-Output (MIMO) transmission, and time domain tails.
It would therefore be desirable to be able to provide a system that enjoys the benefits of OFDMA/SC-FDMA as its core waveform and yet offers the capability of asynchronous communication.